Attend an event important to your loved one. Even if it is something you are not remotely interested in, go out of support for your friend, spouse, child, brother, sister, or parent.
Attend your niece's ballet recital, even if you have to sit through 3 hours of other people's kids dancing just to see your niece's five minutes of fame. Go to your baby brother's orchestra concert, or your best friend's graduation, or your parent's favorite musical theater production. Do it because you love your friend or relative, not necessarily because you love the event itself.
You might surprise yourself and find that what interests them actually interests you, too! Regardless, simply by showing up, you are showing that person how much you care for them by taking the time to be there with and for them.
If your loved one is participating in a performance, surprise them afterward with flowers and words of praise. Or take your niece out to ice cream after her recital to celebrate. Bring her whole dance class! If it's allowed, tape the performance and relive the moment again later.
If you don't have time to attend yourself, invite their friend to go with them instead and pay for the friend's ticket--you are still giving the gift of the experience to your loved one in a kind gesture. Or offer to take them to and from the performance so they don't have to worry about parking. If it is a performance that your loved one is in that you have to miss, request someone else to tape it and you can watch it together at a later date.
If you say you will go, then keep your word and go. Here are some simple suggestions on how to keep your promises.